Enable/disable ironic in tempest config

In order to run tempest tests for Ironic in devstack
the availability of the Ironic service must be set in
the tempest config.

This patch adds a shortcut for Ironic services and sets
availability of Ironic in tempest config.

Change-Id: I206fc2ea13412ceb128f8bfe90c153348d6f2f3e
Merge "Enable/disable ironic in tempest config"